1. Field of the Invention
The present invention relates to a hydraulic control device of controlling an actuator provided on a working machine such as a hydraulic excavator, and particularly to a hydraulic control device of a working machine suitable for controlling a swinging operation.
2. Description of the Related Art
Conventionally, in the hydraulic excavator as the working machine, when attachments such as a swing motor, a travel motor, a boom cylinder, an arm cylinder, a bucket cylinder and so on are operated, an operating lever is operated to a full lever at a stretch, a lever operating amount is held constant, or the operating amount is somewhat changed while operating the actuator in a constant amount.
When the response of the actuator to the lever operation is excessively sensitive, there involves inconveniences such that when in operation, the actuator is actuated with the shock; it is difficult to hold the lever operating amount constant; or when the lever operation is changed in slight amount, the actuator sensitively reacts therewith to bring forth hunting. It is difficult for an unskilled operator to handle such a sensitively operating actuator as described. Then, an attempt has been made wherein a bleed-off passage of a control valve designed so that when the full lever operation is made, it is normally fully closed is made in a slightly open state even at the full lever operation, thereby improving the operativeness.
For example, in Japanese Patent Application Laid-Open No. 9-165791 Publication, there is shown a constitution in which in the full lever operation, a predetermined flow rate is discharged to a tank from a hydraulic pump, as shown in FIG. 10. In FIG. 10, reference numeral 60 designates an engine; 61 and 62 a first hydraulic pump and a second hydraulic pump driven by the engine 60; 63 a cylinder for an earth-discharge plate; 64 a swing motor; 65 an arm cylinder; 66 a left travel motor; 67 a bucket cylinder; 68 a swing cylinder; 69 a boom cylinder; and 70 a right travel motor. Direction control valves are disposed on a center bypass line 71 connected to the first hydraulic pump 61, and a direction control valve 73 for an arm is connected in tandem at the downstream side of a direction control valve 72 for swing. The direction control valve 72 for swing is provided with a throttle 72a forming a bleed-off opening.
According to this constitution, in the full lever operation, the direction control valve 72 for swing bleeds off a part of pressure oil, and where single driving of the swing motor 64 is switched to composite driving of the swing motor 64 and the arm cylinder 65, the flow rate discharged from the throttle 72a is supplied to the arm cylinder 65 through a direction control valve 73 for an arm positioned at the downstream of the direction control valve 72 for swing. At this time, the flow rate substantially equal to that at the swing single driving is supplied to the swing motor 64. Accordingly, it is possible to prevent rapid swing operation in the swing single driving, and in the composite driving, it is possible to prevent the swing speed from being lowered rapidly.
However, since in the aforementioned conventional hydraulic circuit, the bleed-off passage (the throttle 72a) is in a normally open state, when the engine is increased in rotation to discharge a predetermined flow rate of pressure oil from the first hydraulic pump 61, no problem occurs, but since a predetermined flow rate of pressure oil is subject to the bleeding-off, when the rotational frequency of the engine lowers, the flow rate flowing into the swing motor 64 reduces, so that the swing speed lowers.
The concrete work is taken as an example and explained. Where the swing work is carried out on the inclined ground and where an upper swing body is swung toward the upper side of the inclined surface, load applied to the swing motor 54 increases. When the bleed-off passage (the throttle 72a) is opened, the bleed-off flow rate discharged from the bleed-off passage naturally increases, so that the swing speed lowers. Moreover, normally, in the inclined ground, an operator lowers the rotational frequency of the engine for operation in consideration of the stability of the hydraulic excavator. Accordingly, under the conditions as described, it is sometimes that pressure oil necessary for swinging is not sufficiently supplied to the swing motor 64 to stop the swing operation.
A first object of the present invention is to provide a hydraulic control device of a hydraulic working machine, in which for example, in a swing operation, even if full lever operation is carried out, no shock caused by rapid swinging occurs, and a second object thereof is to provide said device, in which for example, in a swing operation, even if the rotational frequency of the engine is lowered, the flow rate necessary for swinging can be supplied to a swing motor to carry out a stable swing operation.
The present invention relates to a hydraulic control device of a working machine having a hydraulic pump driven by a power source, an actuator operated by pressure oil discharged from the hydraulic pump, a control valve for controlling a flow rate and a direction of the pressure oil discharged from the hydraulic pump, and an operating member for switching and operating the control valve, said hydraulic control device of a working machine comprising a bleed-off oil path for bleeding off a part of pressure oil supplied to a specific actuator out of the actuator, a bleed-off amount adjusting means for adjusting a bleed-off amount provided in the bleed-off oil path, an operating amount detecting means for detecting an operating amount of the operating member, and a control means for setting a bleed-off amount according to the operating amount detected by the operating amount detecting means and controlling the bleed-off amount set.
The bleed-off oil path can be constituted by a bypass oil path for communication between an upstream side of the oil path and a downstream side of the oil path of the control valve connected to the specific actuator.
Further, the control valve connected to the specific actuator can be formed with a meter-in passage, a meter-out passage, and said bleed-off oil path as a third passage.
Further, the bleed-off oil path can be constituted by a branch path branched from an oil path which connects the hydraulic pump and the control valve connected the specific actuator.
Further, the bleed-of amount adjusting means can be constituted specifically by a pilot switching valve for opening and closing the bleed-off oil path, and a solenoid proportional valve for exerting a pilot pressure according to the set bleed-off amount on the pilot switching valve.
The control means according to the present invention is possible to control the bleed-off amount adjusting means so that the bleed-off oil path is closed according to the operating amount of the operating member, and when the operating amount reaches a full stroke, the bleed-off oil path is not fully closed.
In the present invention provided with the bypass oil path, if the control valve connected to the specific actuator is designed to intercept the center bypass at the time of switching operation, the control means can be constituted such that the bypass oil path is switched from a full open position to a full closed position with delay for a predetermined time when switching operation is carried out. Further, the control means can be designed so that when the operating amount of the operating member exceeds a first set operating amount, the bypass oil path is gradually closed with delay of time, and when the operating amount of the operating member lowers than a second set operating amount, the closed bypass oil path is released.
In the present invention, where the rotational frequency detecting means for detecting rotational frequency of the power source is present, the control means is possible to control so that when the detected value of the rotational frequency detecting means lowers than a predetermined rotational frequency, the bleed-off oil path is closed.
The control means in the present invention selects a higher degree between the bleed-off amount based on the operating amount detected by the operating amount detecting means and the bleed-off amount based n the rotational frequency detected by the rotational frequency detecting means and control the bleed-off amount adjusting means with the selected bleed-off amount. Further, the control means can control the bleed-off amount adjusting means so that as the rotational frequency of the power source, the bleed-of amount is reduced.
In the present invention, as a concrete example of the specific actuator, a swing motor is shown, and as a control valve connected to the specific actuator, a control valve for swing is shown.
In accordance with the present invention, when the operating member is fully operated, the bleed-off amount adjusting means opens the bleed-off oil path, and bleed-off a part of pressure oil supplied to the specific actuator.
In accordance with the present invention provided with the bypass oil path, when the bleed-off amount adjusting means or the control means fails so that the bleed-off oil path is closed, the pressure oil does not flow into the bypass oil path but the pressure oil flows into the control valve connected to the specific actuator, whereby the specific actuator can be operated continuously. Even in the severe environment for the mechatrosystem working machine involving high temperature, much humidity or much dust, the working machine can be operated stably.
In accordance with the present invention provided with the bleed-off oil path in the control valve, since a part of pressure oil is bled off from the bleed-off oil path formed in the control valve connected to the specific actuator, the circuit constitution is simple.
In accordance with the present invention provided with the branch path at the upstream side of the control valve, since a part of pressure oil supplied to the control valve connected to the specific actuator is bled off on this side of the control valve, the circuit constitution is simple.
In accordance with the present invention in which the bleed-off amount adjusting means comprises a pilot switching valve and a solenoid proportional valve, it is possible to adjust the flow rate of pressure oil flowing in the bleed-off oil path following the operating amount of the operating member.
In accordance with the present invention, when the operating amount of the operating member reaches a full stroke, the bleed-off oil path is not fully closed, whereby the shock caused by the sudden operation can be suppressed.
In accordance with the present invention in which the bypass oil path is closed with delay of time, even if the operating member is operated, the actuator is actuated with delay of predetermined time, whereby the shock caused by the sudden operation can be suppressed.
In accordance with the present invention provided with the rotational frequency detecting means, when the rotational frequency of the engine lowers in a predetermined rotational frequency, the bleed-off oil path is closed, and pressure oil in amount necessary for operation of the actuator is supplied.
In accordance with the present invention in which the rotational frequency of the engine is detected, the bleed-off amount based on the operating amount and the bleed-off amount based on the rotational amount of the engine are selected in high degree, and the bleed-off amount adjusting means is controlled on the basis of the selected bleed-off amount.
Further, since the bleed-off amount can be lowered as the rotational frequency of the engine lowers, the actuator can be operated stably.
In accordance with the present invention in which the specific actuator comprises a swing motor, if the swing operation is carried out suddenly, the shock is suppressed, and other actuators are not affected in operation.